Review and Evaluation of Selected Brand Name Materials for Cleaning Gravestones
by Tracy C. Walther- Architectural Conservator
Some important general guidelines to remember when considering cleaning burial monuments:
- Evaluate the general condition of the burial monument. Do not attempt to clean the monument if it exhibits any cracks, flaking and scaling, or eroding granular surfaces. Carefully sound (gently tap surface with finger) stone to determine if there are any underlying hollow areas. If hollow areas are detected, do not continue with cleaning or handling.
- Determine the type of soiling to remove it in the most effective manner. Types of soiling could be:
Carbonaceous or sooty soiling
Urban grime; dirt
Organic–algae, fungi, lichens, mosses
Stains–metallic, oils, etc.
- Initiate cleaning process with the least aggressive method–gentle, clean water rinsing. If washing with water alone is not sufficient, carefully proceed with the use of a selected material to facilitate cleaning. Select the gentlest possible method that will achieve a desirable or acceptable level of cleanliness.
- Always test selected cleaning method(s) before general application. Test entire cleaning procedure in a small inconspicuous area on the monument.
- Pre-wet monument with water before the application of any chemical cleaning solutions. Pre-wetting prevents excessive penetration of cleaning solutions and soiling into the stone, and facilitates softening of soiling.
- Clean from the bottom to the top of the monument to avoid streak staining on the stone. Periodically rinse runoff.
- Always rinse thoroughly with water. Residues from chemical cleaning solutions can create a blotchy appearance, provide mediums for bacterial action, and cause staining. Do not allow cleaning solutions to dry on a monument.
- Do not assume that a cleaning procedure that is effective in one specific case is therefore applicable for all cleaning situations.
- Consult with a conservation professional.
II. Review and Evaluation of Selected Brand Name Materials for Cleaning Gravestones
Soaps and detergents
- Soaps (e.g., “Ivory”): commercial household detergents (liquids and powders) are not recommended for cleaning masonry. They are rendered insoluble by calcium ions present in stone and hard water. They may also produce free alkali and fatty acid salts.
- Non-ionic Detergents (e.g., Photo Flo – a Kodak product): Non-ionic detergents are recommended for cleaning gravestones. They are electrically neutral cleaning agents that do not contain or contribute to the formation of soluble salts. They provide better wetting of the masonry surface and, therefore, successfully facilitate the removal of general soiling. Non-ionic detergents are available from conservation, janitorial, and photographic suppliers. A suggested cleaning solution is one ounce non-ionic detergent to 5 gallons water.
Acidic Cleaning Materials
- Hydrochloric or Muriatic Acid, Phosphoric Acid (e.g. “Lime Away,” “Naval Jelly”), oxalic acid are not recommended for general cleaning of gravestones. The use of hydrochloric or muriatic acid may result in ferrous chloride (rust) staining and the deposition of soluble salts. Muriatic acid, which is readily available in hardware stores, is a raw acid. It is a by-product of processing steel and contains metallic particles that can cause ferrous staining.
Alkaline, Corrosive, and Biocidal Cleaning Materials
- Sodium Hydroxide (e.g., “Borax”), Sodium Hypochlorite (e.g., “Clorox” “liquid chlorine”) is not recommended for general cleaning of stone.
- Calcium Hypochlorite (e.g., Chlorine, “HTH,” “Shock Treatment”): Calcium hypochlorite or chlorine is effective for the removal of biological growth. It is a granular product that is not to be confused with “liquid chlorine” or sodium hypochlorite. Calcium hypochlorite is available from swimming pool suppliers. A suggested cleaning solution is one ounce calcium hypochlorite to one gallon hot water. This product should be used only when a waterhose with a good water pressure (e.g., 55 psi) is available.
- Ammonium Hydroxide (e.g., household ammonia): Solutions of household ammonia are recommended for cleaning light colored stones. Ammonia is particularly effective for the removal of biological growth. One cup ammonia to one gallon water.
- Quatemary Ammoniums (e.g., algaecides or biocides for swimming pools): Quaternary Ammoniums have a slightly different chemical structure than ammonium hydroxide. They are especially effective for the removal of biological growth, particularly stubborn black algae. Quaternary ammoniums are available from swimming pool suppliers and list ingredients such as alkylbenzyl trimethyl ammonium, benzyl alkyl dimethyl ammonium chlorides, or benzyl aklyl dimethyl ammonium bromides.
- Trisodium Phosphate (e.g., “TSP, “Calgon”): Trisodium phosphate is not recommended for cleaning monuments. It can cause the formation and deposition of soluble salts. “Calgon” contains trisodium phosphate and a number of additives that may be detrimental to monuments.
- “Fantastic” All Purpose Cleaner, “Formula 409,” “Spic and Span” and abrasive cleansers: These are not recommended for cleaning monuments. Avoid products containing sodium chloride, sodium sulfate, sodium carbonate, sodium bicarbonate, and ammonium carbonate, due to their ability to form and deposit soluble salts in monuments.
III. MISCELLANEOUS MATERIALS OR TOOLS
- The following items are recommended for use in cleaning procedures for masonry: soft natural bristle (e.g., tampico) brushes, nylon brushes, tooth brushes, Q-tips, sponges (especially natural sponges). Wood and some plastic spatulas are also recommended.
- Do not use metal brushes or scrapers, or abrasive pads (e.g., “Brillo,” “Scotchbrite”) to clean monuments.
IV. SOME FINAL REMINDERS ABOUT BRAND NAME CLEANING MATERIALS
- Do not rely solely upon product labels or advertising. Brand name materials that are readily available from hardware and grocery stores are generally intended for household use. Information is not provided for specialized applications outside of the home or workshop.
- Remember to consult with a conservation consultant before cleaning. The use of improper cleaning materials and practices can cause serious and irreparable damage to gravestones.
- Further detailed information is found in “A Graveyard Preservation Primer” click here for order information
HOW TO IDENTIFY MAJOR STONE TYPES
- Igneous rock with visible grain, primarily quartz and feldspar
- Speckled appearance with sparkly mica and dull black flecks
- Extremely hard rock that is difficult to carve by hand
- Grays, pinks in a wide range of colors
- Commercial granite’s include gneiss and other rocks not strictly granite
- Exhibits a full range of grain sizes with uniform surface patterns
- Granular with no discernible bedding planes
- Often used for monuments and tombs
- Soft, sedimentary rock primarily composed of calcite
- Fossils may be recognizable and are the most diagnostic trait
- Tan, buff or gray colored that darkens with age
- Matte surface almost never polished
- Somewhat rough texture, like marble
- No marked veining like marble
- No definite layers or bedding planes like sandstone
- No sparkly mica grains like granite
- Often gets gypsum crusts
- Hard, dense crystalline or granular metamorphic limestone
- White when new or in new breaks, but older marbles may appear gray from soiling
- Capable of taking a high polish, yellows with age
- May have veins of gray or gold
- Commercial marble is any lime carbonate capable of taking a polish, could include limestone and many colors
- Tennessee marble is medium-grained similar to limestone in texture with a pink cast
- Georgia marble is very large-grained, somewhat gray in color
- Predominant stone for gravestones in the 19th century
- Many early marbles are eroded and sugaring
- Sedimentary rock composed of cemented sand grains bedding planes
- Red and brown (Brownstone) in color, can be gray, tan or blue (Bluestone)
- Fine-grained stone with sand grains
- Often flakes and delaminates
- Metamorphosed shale, hard and brittle
- Usually black, gray or blue
- Sometimes fades with time
- Extremely smooth, fine-grained stone with even bedding planes usually running parallel with the stone face
- Holds carving very well, inscriptions usually very clear
- Uniform surface appearance
- Gravestones tend to be thin and simple in shape, generally not more than six inches
- Metamorphic rock
- Largely composed of the mineral talc and is rich in magnesium
- Easily carved and darkens over age
- Smooth to the touch
- Used in 19th century, commonly for slot and tab tombs in Georgia
- White, gray, greenish gray, pale green — commonly discolored in reddish or brownish hues and mottled
Tools and Materials for Gravestone Cleaning Projects
by Fannin Lehner Preservation Consultants
- Marble and Limestone
- Non-ionic Detergent (Photo-Flo-Kodak product)
- Household Ammonia (Requires water hose for rinsing and Hydration Paper test strips for pH testing.)
- Calcium Hypochlorite (HTH) for biological growth retardation. (Requires water hose for rinsing and Hydration Paper test strips for pH testing.)
- Slate and Other Stone
- Non-ionic Detergent (Photo-Flo-Kodak product)
- Good water supply
- Non-ionic Detergent (Photo-Flo–Kodak product).
- 1/4 oz./5 quarts water
- Ammonia–1 cup/1 gal. water (for marble only)
- Calcium Hypochlorite (granular)-2 oz. dry/1 gal. warm water
- Assortment of brushes (NOT WIRE) of varying stiffness.
- Toothbrushes (firm), sponges
- Scrapers – craft sticks, plastic scrapers
- Kaolin/porcelain clay (dry),
- Glycerin (use 50/50 mixture with water)
- Saran Wrap and heavy plastic for wrapping
- Tape / string to secure plastic
- Scrapers – plastic and wood
- Wire brushes, metal instruments, abrasive pads (Scotchbrite, Brillo, Steel wool)
- Acid or acidic cleaners (especially on marble or limestone!) (Should only be used by conservators with proper training on non-calcareous stone)
- Household cleaners: soap (Ivory), detergents (liquid or powder), Borax, Clorox, TSP, Calgon, Fantastik, Formula 409, Spic and Span (or any other abrasive cleaner)
REMEMBER: The use of improper cleaning materials and practices can cause serious and irreparable damage to gravestones! Make sure the stone is stable before attempting to clean it – no flaking, delaminating, etc.